First stab at getting guard to cleanly watch for inotify events outside of a Vagrant VM, send the event inside and report back on the outside again. See comments for more description.

Guardfile

require 'guard'
require 'guard/guard'
require 'guard/jasmine-node'

module ::Guard
  class Guard
    def vagrant_run_prefix() 
      prep_ssh_config
      "ssh -F #{ssh_conf_file} default -- cd /vagrant\\;"
    end

    def stop()
      clean_ssh_config
      super
    end

  protected

    # "vagrant ssh" is exceptionally slow, so we do some 
    # hackiness here to pull out the ssh_config from vagrant
    # and translate it for use during our session
    @tempdir = nil
    def get_temp_dir()
      if @tempdir.nil?
        @tempdir = `mktemp -d /tmp/VagrantGuard.XXXXXX`
        @tempdir.strip!
      end
      @tempdir
    end

    def get_ssh_config()
      known_hosts_file = File.join(get_temp_dir, 'known_hosts')
      conf = `vagrant ssh-config`
      conf.gsub!(/^(\s*UserKnownHostsFile).*$/, "\\1 #{known_hosts_file}")
    end

    def ssh_conf_file()
      File.join(get_temp_dir, 'ssh_config')
    end

    @ssh_prepped = false
    def prep_ssh_config()
      if ! @ssh_prepped 
        conf = get_ssh_config
        File.open(ssh_conf_file, 'w') { |file|
          file.write(conf)
        }
        @ssh_prepped = true
      end
    end

    def clean_ssh_config()
      if @ssh_prepped
        @ssh_prepped = false
        `rm -rf -- #{@tempdir}`
        @tempdir = nil
      end
    end
  end

  # hack in to JasmineNode our ssh prefix
  class VagrantJasmineNode < JasmineNode
    def start()
      DEFAULT_OPTIONS[:jasmine_node_bin] = 
        vagrant_run_prefix + 'node_modules/jasmine-node/bin/jasmine-node'
      super
    end
  end
end

guard 'VagrantJasmineNode' do
  watch(%r{^spec/(.+)\.spec\.js$}) { |m| "#{m[0]}" }
  watch(%r{^lib/(.+)\.js$})        { |m| "spec/lib/#{m[1]}.spec.js" }
end

# vim: ft=ruby ts=2 sw=2 et

What's happening:

• Guard watches files on the parent host (so inotify "just works")
• Guard is slightly modified to know how to SSH in to the Vagrant VM (at least slightly hacky - doesn't use "vagrant ssh" just because it's soooooooooooo slooooooooooooooooowwwww)
• We overload calls in JasmineNode to run them over SSH (super hacky)
• JasmineNode ends up parsing the output as per usual (so NotifySend "just works")

I think feasibly this could be turned in to a plugin given a bit more love, at the moment it can be run directly as a Guardfile (but has some limitations about the parent host for now - e.g. won't work on Windows in its current form). In current form I'd obviously need to overload every Guard test driver available - but maybe there's a more general pattern for overloading them?

This method is quite different from the normal approaches I've seen people trying, including NFS mounts (not portable, difficult to set up), forcing Guard to poll (CPU intensive) and redirecting notifications from within the VM over ssh with vagrant-notify ("oh my eyes, they burn they burn!").

Keen to know if anyone can do this better.